net_sched: RCU conversion of stab
This patch converts stab qdisc management to RCU, so that we can perform
the qdisc_calculate_pkt_len() call before getting qdisc lock.
This shortens the lock's held time in __dev_xmit_skb().
This permits more qdiscs to get TCQ_F_CAN_BYPASS status, avoiding lot of
cache misses and so reducing latencies.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
CC: Jesper Dangaard Brouer <hawk@diku.dk>
CC: Jarek Poplawski <jarkao2@gmail.com>
CC: Jamal Hadi Salim <hadi@cyberus.ca>
CC: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index a4ccd47..2730352 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2325,15 +2325,18 @@
struct netdev_queue *txq)
{
spinlock_t *root_lock = qdisc_lock(q);
- bool contended = qdisc_is_running(q);
+ bool contended;
int rc;
+ qdisc_skb_cb(skb)->pkt_len = skb->len;
+ qdisc_calculate_pkt_len(skb, q);
/*
* Heuristic to force contended enqueues to serialize on a
* separate lock before trying to get qdisc main lock.
* This permits __QDISC_STATE_RUNNING owner to get the lock more often
* and dequeue packets faster.
*/
+ contended = qdisc_is_running(q);
if (unlikely(contended))
spin_lock(&q->busylock);
@@ -2351,7 +2354,6 @@
if (!(dev->priv_flags & IFF_XMIT_DST_RELEASE))
skb_dst_force(skb);
- qdisc_skb_cb(skb)->pkt_len = skb->len;
qdisc_bstats_update(q, skb);
if (sch_direct_xmit(skb, q, dev, txq, root_lock)) {
@@ -2366,7 +2368,7 @@
rc = NET_XMIT_SUCCESS;
} else {
skb_dst_force(skb);
- rc = qdisc_enqueue_root(skb, q);
+ rc = q->enqueue(skb, q) & NET_XMIT_MASK;
if (qdisc_run_begin(q)) {
if (unlikely(contended)) {
spin_unlock(&q->busylock);
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 374fcbe..1507415 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -398,6 +398,11 @@
return stab;
}
+static void stab_kfree_rcu(struct rcu_head *head)
+{
+ kfree(container_of(head, struct qdisc_size_table, rcu));
+}
+
void qdisc_put_stab(struct qdisc_size_table *tab)
{
if (!tab)
@@ -407,7 +412,7 @@
if (--tab->refcnt == 0) {
list_del(&tab->list);
- kfree(tab);
+ call_rcu_bh(&tab->rcu, stab_kfree_rcu);
}
spin_unlock(&qdisc_stab_lock);
@@ -430,7 +435,7 @@
return -1;
}
-void qdisc_calculate_pkt_len(struct sk_buff *skb, struct qdisc_size_table *stab)
+void __qdisc_calculate_pkt_len(struct sk_buff *skb, const struct qdisc_size_table *stab)
{
int pkt_len, slot;
@@ -456,7 +461,7 @@
pkt_len = 1;
qdisc_skb_cb(skb)->pkt_len = pkt_len;
}
-EXPORT_SYMBOL(qdisc_calculate_pkt_len);
+EXPORT_SYMBOL(__qdisc_calculate_pkt_len);
void qdisc_warn_nonwc(char *txt, struct Qdisc *qdisc)
{
@@ -835,7 +840,7 @@
err = PTR_ERR(stab);
goto err_out4;
}
- sch->stab = stab;
+ rcu_assign_pointer(sch->stab, stab);
}
if (tca[TCA_RATE]) {
spinlock_t *root_lock;
@@ -875,7 +880,7 @@
* Any broken qdiscs that would require a ops->reset() here?
* The qdisc was never in action so it shouldn't be necessary.
*/
- qdisc_put_stab(sch->stab);
+ qdisc_put_stab(rtnl_dereference(sch->stab));
if (ops->destroy)
ops->destroy(sch);
goto err_out3;
@@ -883,7 +888,7 @@
static int qdisc_change(struct Qdisc *sch, struct nlattr **tca)
{
- struct qdisc_size_table *stab = NULL;
+ struct qdisc_size_table *ostab, *stab = NULL;
int err = 0;
if (tca[TCA_OPTIONS]) {
@@ -900,8 +905,9 @@
return PTR_ERR(stab);
}
- qdisc_put_stab(sch->stab);
- sch->stab = stab;
+ ostab = rtnl_dereference(sch->stab);
+ rcu_assign_pointer(sch->stab, stab);
+ qdisc_put_stab(ostab);
if (tca[TCA_RATE]) {
/* NB: ignores errors from replace_estimator
@@ -1180,6 +1186,7 @@
struct nlmsghdr *nlh;
unsigned char *b = skb_tail_pointer(skb);
struct gnet_dump d;
+ struct qdisc_size_table *stab;
nlh = NLMSG_NEW(skb, pid, seq, event, sizeof(*tcm), flags);
tcm = NLMSG_DATA(nlh);
@@ -1195,7 +1202,8 @@
goto nla_put_failure;
q->qstats.qlen = q->q.qlen;
- if (q->stab && qdisc_dump_stab(skb, q->stab) < 0)
+ stab = rtnl_dereference(q->stab);
+ if (stab && qdisc_dump_stab(skb, stab) < 0)
goto nla_put_failure;
if (gnet_stats_start_copy_compat(skb, TCA_STATS2, TCA_STATS, TCA_XSTATS,
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 2f1cb62..cc17e79 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -632,7 +632,7 @@
#ifdef CONFIG_NET_SCHED
qdisc_list_del(qdisc);
- qdisc_put_stab(qdisc->stab);
+ qdisc_put_stab(rtnl_dereference(qdisc->stab));
#endif
gen_kill_estimator(&qdisc->bstats, &qdisc->rate_est);
if (ops->reset)